This application is based upon, claims the benefit of priority of, and incorporates by reference, the contents of Japanese Patent Applications No. 2001-232390 filed Jul. 31, 2001, and No. 2002-123317 filed Apr. 25, 2002.
1. Field of the Invention
The present invention relates to a fuel pump constructed such that a fixed shaft is at the center of a housing, and a motor unit and a pump unit rotate about the fixed shaft.
2. Description of Related Art
Japanese Patent Laid-Open Publication No. Sho. 63-82086 discloses a fuel pump. Generally, in this fuel pump, as shown in FIG. 4, a fixed shaft 12 is fixed at the center of a housing 11. Bearing members 16 are individually pushed into and fixed to an inner periphery of both ends of a pipe member 15 provided at the center of an armature 14 (a rotor) of a motor unit 13. These bearing members 16 are rotatably inserted over the fixed shaft 12 to rotatably support the pipe member 15 with the fixed shaft 12 through the bearing members 16. In this case, the bearing members 16 are pushed into and fixed to the inner periphery of the pipe member 15, thereby positioning the bearing members 16 between the pipe member 15 and the fixed shaft 12. An impeller 18 in a pump unit 17 is fitted and fixed to the pipe member 15, and the armature 14 of the motor unit 13, the pipe member 15, and the impeller 18 integrally rotate about the fixed shaft 12.
However, in the conventional construction described above, since the motor unit 13 and the pump unit 17 are arranged with a gap provided therebetween in the axial direction in the housing 11, the dimension of the fuel pump becomes large along its axial direction.
In the conventional construction described above, it is necessary to provide spaces for interposing the bearing members 16 between the pipe member 15 for supporting the armature 14 of the motor unit 13, and the fixed shaft 12. Accordingly, the outer diameter of the pipe member 15 increases, and storage space for the armature 14 decreases in the housing 11. As a result, space for armature windings decreases, motor output decreases, and discharge capability of the pump also decreases. On the other hand, when the outer diameter of the housing 11 is increased to secure the winding space of the armature 14, and to prevent decrease of the motor output and to prevent decrease of the discharge capability, the outer diameter of the fuel pump increases.
In the conventional construction described above, the outer peripheral surface of the bearing members 16 is pressed against the inner peripheral surface of the pipe member 15, and the inner peripheral surface of the bearing members 16 is slidably in contact with the outer peripheral surface of the fixed shaft 12. Because of this, precision in dimension and concentricity is required both for the inner diameter and the outer diameter of the bearing members 16. When the precision of the inner diameter and the outer diameter of the bearing members 16 decreases in dimension and concentricity, the assembly of the fuel pump becomes difficult. Additionally, the armature 14 may vibrate and noise may be generated when the fuel pump is in operation. Thus, it is necessary to precisely machine both the inner diameter and the outer diameter of the bearing members 16 to secure the precision of the inner diameter and the outer diameter in dimension and concentricity. As a result, the time and costs associated with machining the bearing members 16 may increase, and the overall manufacturing cost of the fuel pump may increase.
A first object of the present invention is to decrease the axial dimension of the fuel pump. A second object of the present invention is to reduce the diameter of the pipe member, which supports the armature of the motor unit, to increase the storage space for the armature in the housing, to increase the pump discharge capability, and to reduce the outer diameter of the fuel pump. A third object of the present invention is to simplify the machining of the bearing members while maintaining precision in dimension and concentricity required of the bearing members. Finally, reducing machining costs is desired.
In a first aspect of the invention, a fuel pump of the present invention includes a pump unit for drawing and discharging fuel, a motor unit for driving the pump unit, a housing for housing the pump unit and the motor unit, a fixed shaft fixed at the center of the housing, a pipe member provided at the center of an armature of the motor unit, and inserted over the fixed shaft, and bearing members individually used for rotatably supporting both ends of the pipe member on the fixed shaft. A part of said armature and a rotational body of the pump unit are arranged on the bearing members located on the side of the pump unit such that they are overlapped with each other to integrally rotate. With this construction, the storage space for the motor unit and the pump unit decreases in the axial direction in the housing, and the axial dimension of the fuel pump decreases.
In one regard, it is preferable to form the fuel pump such that the part of the armature overlapped with the rotational body of the pump unit is engaged with the rotational body to transmit a rotational force of the armature to the rotation body. With this construction, the engagement structure (a coupling structure) between the armature and the rotational body of the pump unit is compactly formed on the bearing member. In another regard, it is preferred that the part of the armature overlapped with the rotational body of the pump unit be made of a resin.
To attain the second object, in another aspect, the ends of the pipe member may be placed between the fixed shaft and the bearing members. With this construction, it is not necessary to provide spaces for interposing the bearing members between the pipe member and the fixed shaft, and the outer diameter of the pipe member can be reduced accordingly. As a result, the storage space for the armature in the housing can be increased, the winding space for the armature can be increased, and the motor output and the pump discharge capability can be increased. In other words, even when the outer diameter of the housing is made small, the winding space secured for the armature is almost as large as that in the conventional case. Additionally, the outer diameter of the fuel pump can be reduced while the discharge capability of the pump can be maintained at the conventional pump level.
To attain the third object, in another aspect, a through hole in a step shape may be formed at the center of the bearing members. Additionally, the fixed shaft may be rotatably inserted into a part of the through hole with a smaller diameter (referred to as a xe2x80x9csmall diameter holexe2x80x9d), and a part of the through hole with a larger diameter (referred to as a xe2x80x9clarge diameter holexe2x80x9d) may support the ends of the pipe member. With this construction, since it is not necessary to provide spaces for interposing the bearing members between the pipe member and the fixed shaft, beneficial effects can be obtained.
Since the large diameter hole for supporting the pipe member and the small diameter hole for inserting over the fixed shaft are formed concentrically on the inner peripheral side of the bearing members, the inner peripheral side of the bearing member is machined using a cutting tool while the outer periphery of the bearing member is held by a chuck during machining of the bearing members. Thus, the large diameter hole for supporting the pipe member and the small diameter hole for inserting over the fixed shaft are precisely formed on the inner peripheral side of the bearing members while the shaft centers of both of the holes precisely coincide with each other. Consequently, machining the bearing members becomes simple while dimensional accuracy and precise concentricity required for the bearing members is secured. Additionally, machining costs decrease.
In this case, though an independent member may be interposed between the large diameter hole of the bearing members and the ends of the pipe member, it is preferable that the ends of the pipe member be pushed into and fixed to the large diameter hole of the bearing members. This construction makes the shaft center of the pipe member precisely coincide with the shaft center of the large diameter hole of the bearing member. Thus, the precision in concentricity among the pipe member, the bearing members, and the fixed shaft increases compared with the case where the independent member is interposed between the large diameter hole of the bearing members and the ends of the pipe member. Additionally, runout of the armature caused by the low concentricity (non-concentric condition) can be prevented.
In the structure for supporting the rotational body of the pump unit, though the rotational body of the pump unit may be inserted over the fixed shaft, sliding friction is generated between the fixed shaft and the rotational body. As a result, pump performance decreases accordingly, and the rotational body may be fused to the fixed shaft because of frictional heat when the rotational body is formed of a resin.
In consideration of this, a guide hole slightly larger than the outer diameter of the bearing member is formed at the center of the rotational body of the pump unit. The bearing member is fitted into the guide hole of the rotational body. Coupling protrusions provided on the armature of the motor unit are engaged with engagement parts formed on the rotational body. Thereby the rotational force of the armature is transmitted to the rotational body. With this construction, the rotational body of the pump unit rotates while the rotational body is guided by the outer peripheral surface of the bearing member which rotates integrally with the armature. Thus, the rotational friction of the rotational body decreases, the pump performance increases accordingly, and the fusion of the rotational body to the bearing member caused by frictional heat can be prevented even when the rotational body is made of a resin.
Additionally, a pump cover may constitute an end surface of the housing on the motor unit side, and a fixing hole for fixing the end of the fixed shaft may be formed on the pump cover. In addition, a tapered part may be formed on the side of the motor unit in the fixing hole. With this construction, the tapered part guides the end of the fixed shaft to the fixing hole on the pump cover when the end of the fixed shaft is inserted into, or pushed into, the fixing hole on the pump cover in a manufacturing and assembling process of the fuel pump. Thus, the operation for inserting or pushing the end of the fixed shaft into the fixing hole on the pump cover is facilitated.
Again, the pump cover may be made of a resin. With this construction, the requirement of reducing the manufacturing cost, and reducing part weight is satisfied. When the housing is made of a resin, the housing including the pump cover may be integrally formed with the resin.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.